Spinal deformities of varying etiologies are well known. Such deformities include abnormal spinal curvatures, such as, for example, scoliosis, kyphosis, or other abnormal curvatures wherein natural alignment of the spine is altered. Specifically, scoliotic deformities can be separated into abnormal translation and/or rotation of the vertebrae in each of the coronal, transverse, and sagittal planes. Therefore, treatment of certain spinal deformities such as scoliosis may require addressing reduction of the abnormal curvature in each of the three spatial planes.
A number of methods and techniques have been used to reduce abnormal spinal curvatures. Several of these techniques have been based on anchoring a devise onto posterior elements of the spine. Such techniques may reduce the certain translational aspects of the deformity, but have little or no effect on the rotational aspects.
Additionally, pedicle screws have been used in the treatment of abnormal spinal curvatures. Such techniques are based on translation to align the spinal column, either by bending or rotating a fixation rod after the rod is engaged to the pedicle screws, or by forcing the pedicle screws into engagement with the rod. Other reduction techniques provide for derotation via the use of pedicle screws, but such derotation is usually implemented following placement of the fixation rod.